Iron-air batteries are well known in the art, and taught, for example, by Chottiner, in U.S. Pat. No. 4,152,489. These batteries can utilize air as an oxidant reactant. The air contacts an electrode made of an outer hydrophobic membrane, laminated to an active hydrophilic layer. The electrode hydrophilic layers can contain carbon particles, catalyst, low oxygen overvoltage material, Such as WC, and binder, pasted into a fiber metal plaque. These batteries usually contain an iron fuel electrode, immersed in potassium hydroxide electrolyte, and disposed between a set of air electrodes. The iron electrode can contain a mixture of iron oxides, for example Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4, with reaction promoting compounds and dispersing agents, pasted into diffusion bonded, nickel-plated steel plaques, as taught by Seidel, in U.S. Pat. No. 3,849,198. The iron electrode can also be self supporting, and contain sintered metallic iron particles coated with a metal sulfate, such as MgSO.sub.4, as taught by Buzzelli et al., in U.S. Pat. No. 4,132,547.
Iron-air batteries have been considered as a power source for electrically run automobiles. These type batteries have a very high energy-to-density ratio, and are thus more attractive than standard lead acid batteries presently used as an engine starting source in automobiles. One of the main problems associated with battery-driven vehicles, however, is that, unlike the gasoline or diesel-fueled automobile where the fuel tank can be refilled in minutes, battery recharging may take from 2 to 10 hours. For commuter applications, the electrically rechargeable battery may be acceptable, where the vehicle can be parked overnight near a recharging source. It is unacceptable, however, for long distance interstate travel. What is needed, to make such a battery-driven vehicle competitive, and commercially useful, is a battery power system that can be recharged in from about 15 to 30 minutes.
Oswin recognized this problem in U.S. Pat. No. 3,479,226. The Oswin cell, while containing removable, metal anodes, utilized in-situ recharging. There, the air electrode would be connected to an in-place hydrogen-depolarized, consumable anode, more electronegative than hydrogen in alkali electrolyte, for example, cadmium, copper, nickel, cobalt, lead, or bismuth, and then swept with hydrogan gas. If zinc or iron were to be used as the anode, a suitable voltage would have to be applied, essentially defeating the purpose of the inventon, since an external generator would be needed. In this second instance the anode was not removed for recharging.
In Oswin, the results were anodic oxidation of hydrogen at the air electrode and cathodic reduction of metal oxide at the metal electrode. Here, a sintered or sheet metal anode fits inside a bi-cathode air electrode sheath with an electrolyte saturated separator therebetween. Recharging time was approximately 2 hours utilizing a cadmium anode and 21/2 hours using a zinc anode, where a DC power source was required to apply an appropriate voltage. In such a method, using a series of cells in battery configuration, air vents to the air electrode would have to be closed, and remaining oxygen removed by a nitrogen flush before introducing hydrogen.
Chodosh, in U.S. Pat. No. 3,457,488, teaches a battery, and an electrode construction somewhat similar to that of Oswin. Chodosh completely removes the consumable anode, places it in an external electrolyte bath, and electrically recharges it against a suitable counterelectrode, such as a nickel sheet, using a DC power source. Suitable anode materials are selected from sintered lead, iron, cadmium, aluminum, magnesium, and preferably zinc. Such electrical recharge external to the battery, though it could be recharged rapidly, i.e., at gassing potential, would still probably take about 1 hour. What is needed is an even quicker method to get battery-powered cars recharged and back on the road.